To obtain the body of knowledge that everyone throughout history that has ever wanted to convert couchbase to csv : couchbase convert to csv - Google Search
The bottom line is that CSV is only two dimensional, whereas json can b n-dimensional, there is no obvious conversion. You’ll have to make your own.
Google for “converting Json to comma-separated in Java” (without the quotes).
you could also do it in n1ql with "SELECT RAW … " and constructing a single projected property which is a comma-separated string of the properties.
You could also export as json, and pipe that through jq.